It's not just that.

Aboriginal people died at a rate of 0.13 per 100 prisoners, compared to a death rate of 0.21 per 100 prisoners for the total prison population.

[...]

The same AIC report calculated that Indigenous people as a whole died in police custody at more than six times the rate of non-Indigenous people as a whole – 0.61 per 100,000 people, compared to 0.09 per 100,000 people.

As a prison population, they don't die at a higher rate. As a whole peoples they do.

https://www.theguardian.com/australia-news/2021/apr/09/the-facts-about-australias-rising-toll-of-indigenous-deaths-in-custody